Production of metals by electrolysis



PRODUCTION OF METALS BY ELECTROLYSIS Filed United States Patent 3 006 824 PRODUCTION or M ETA LS BY ELECTROLYSIS Joseph B. Story, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 29, 1958, Ser. No. 764,028 2 Claims. (Cl. 204-59) This invention relates to the electrolytic production of metals and metal compounds from metal salts. More specifically the invention relates to an electrolytic method, and apparatus, for producing substantially pure metals from fused and aqueous salt solutions.

Cells are generally divided into two types; mercury cathode and diaphragm. For economic operation the distance between the anode and cathode is kept as close as possible since greater distances require commensurately higher cell voltages. When, however, the distances between the anode and cathode is small there occurs recombination and side reactions of the products formed which greatly reduced the current efficiency of the cell, contaminate the products, and oxidize the anode electrodes. Thus, it is desirable to bring the anode and cathode as close together as possible and yet the separation of the anode and cathode is essential.

One attempt to solve this problem resulted in the diaphragm type of cell. In this type of cell the electrodes are kept separated by a diaphragm consisting of substantially non-charged materials such as asbestos, ceramic materials and the like. Foraminous metal diaphragms are also used in this manner but no potential is applied thereto. This allows ions to pass through by electrical migration but reduces diffusion of the products. Diaphragm cells have been partially successful and they permit the construction of compact cells of lower resistance in that the cathode and anode or electrodes can be placed closer together.

Other attempts to solve the problem have resulted in the mercury cathode or amalgam type cell. Many variations of this type of cell has been proposed in order to make the electrolysis as simple and eificient as possible. In this type of cell the free metal of the salt to be processed is electrolytically deposited into the mercury cathode to form an amalgam, and the amalgam is then withdrawn from the electrolysis compartment. The amalgam is then processed in a separate compartment to remove the deposited metal. The difiiculties inherent in this type of process result from the weak concentrations of the metal amalgamating with the mercury and the necessity of having to transfer the amalgam to a separate processing chamber. If a pure metal is desired it is necessary in most instances to recover it by distillation of the mercury therefrom. Because of the small amount of the metal within the mercury this is obviously quite expensive.

It is therefore an object of the present invention to provide an electrolysis process for the more eflicient and more economic production of metals. More specifically, it is an object of the present invention to provide an electrolysis process for the production of metals from their fused salts or from their solutions more economically and also to obtain purer products. Another object of the present invention is to provide an electrolytic cell which permits the passage of the cathode of cations of the salt being treated but eliminates diffusion of the products. Yet another object of the present invention is to provide a new type electrolytic cell which combines the best features of both the diaphragm type and the mercury cathode or amalgam type cell. A yet further object of the present invention is to provide a cell with all the advantages of an amalgam type cell but one wherein there is no necessity for the transfer of the ice amalgam to a separate decomposition compartment. Other objects will appear hereinafter.

In the drawings, FIGURES l and 2 illustrate two of the apparatus embodiments of the present invention.

FIGURE 1 is a sectional elevation of a cell used for the recovery of a metal from an electrolyte solution in which a thin supported mercuric film is interposed between the anode and cathode.

FIGURE 2 is a half sectional elevation view of a round cell having a central bottom mounted anode surrounded by a steel cell shell which constitutes the cathode. A thin film of molten lead is supported on a lioraminous metal diaphragm which is concentric with the anode and cathode and substantially centrally located between these members.

In its essence, the apparatus of the invention provides for the formation of an anode and a cathode compartment by the separation of the anode and cathode by a thin supported film of liquid or molten metal which is non-reactive with the electrolyte bath at processing conditions. Referring to the electrolyte in the anode compartment as the anolyte portion and to the electrolyte in the cathode compartment as the catholyte portion, the process of the invention in its broadest form provides; maintaining dissolved in the anolyte portion the salt of a metal, the metallic portion of which is soluble within the said thin supported film of metal, while passing an elec tric current through the anolyte and catholyte and thereby depositing the metal from the dissolved salt in the anolyte into the thin supported film of metal and then recovering the deposited metal from the catholyte portion of the electrolyte bath. In accordance with principles here inafter described it is possible to recover the deposited metal from the catholyte portion of the electrolyte bath either in the form of a pure metal or as a reaction product of that metal.

In a preferred embodiment of the invention an electrolyte composition, which is to be decomposed, is introduced in to the anolyte portion of the electrolyte bath. A similar or dissimilar electrolyte composition, dependent upon principles defined hereinafter, is introduced into the catholyte portion of the electrolyte bath. Upon passing an electric current through the electrolyte bath the cations within the anolyte portion migrate to, and are deposited into the thin supported film of metal which separates the anolyte portion and the catholyte portion. On the opposite side of the film, i.e., on the side of the film in contact with the catholyte portion, the deposited cations are removed. The manner of removal is dependent upon whether it is desirable to recover the deposited metal in its metallic form or in the form of some reaction product of the said metal. This aim also determines the nature of the electrolyte of the catholyte portion of the electrolyte bath. Thus, if it is desired to recover the metallic metal in pure form then the catholyte portion must be non-reactive with that metal and in addition the cations of the catholyte portion must be of the same metal as the pure metal to be recovered even though the cation concentration of the catholyte portion is not substantially depleted during the process. On the other hand it may be desirable to form a reaction product with the deposited metal. In this case all that is necessary is to provide a catholyte portion which reacts with the deposited metal to give the desired product. The eflect of the thin supported film of metal is to completely prevent the passage of products from the catholyte portion to the anolyte portion. It allows only for the passage of cations from the anolyte portion to the catholyte portion. Contamination of the catholyte portion by diffusion of materials from the anolyte portion is completely eliminated. Passage of cations which are insoluble in the thin supported film of metal is also prevented. This creates a substantially pure product.

The fundamental nature of the thin supported film of metal is its ability at operating conditions to dissolve, or in the case of mercury to amalgamate, the metal within the anolyte portion which is to be treated or recovered while preventing diffusion of products between the anolyte portion and the catholyte portion. It thus acts as a grid or semi-permeable partition in that it permits the passage of a selected group of cations from the anolyte portion into the eatholyte portion for recovery. Mercury is a suitable metal for the separation and recovery of the metals of salts which are amalgamable therewith. It cannot be used however in most fused electrolyte baths because of its low boiling point. It is a highly preferred medium for the separation of salts of amalgamable metals in solution. In a fused electrolyte bath a metal is selected which is liquid at the operating temperature, is unreactive with the electrolyte bath, but will dissolve the metal of the salt which is to be processed. Molten tin, silver, cadmium, or lead, for example, will form a suitable means for the separation of the salts of metals, the metallic portion of which is soluble therein.

The process of this invention, as well as suitable apparatus or cells for carrying out the process will become apparent after considering the following detailed description.

Referring to FIGURE 1, there is shown an electrolytic cell 11 provided with an anode l2 and cathode 13 (electrical leads not shown). The anode 12 and cathode 13 are separated by a continuous thin supported film of metal 16 which divides the cell into two separate compartments. These compartments, each containing an electrolyte into which an electrode is immersed thus form an anolyte portion 14 and catholyte portion 15. For convenience of illustration, as well as for purposes of showing a highly preferred embodiment, the following describes the method for recovering a substantially pure metallic product from a solution, in this instance sodium, though other metals can be similarly recovered as will 'be explained hereinafter. The anolyte portion 14- then -contains an aqueous sodium chloride solution and the 'catholyte portion 15 contains a diethylene glycol dimethyl ether solution of sodium iodide. In this instance diethylene glycol dimethyl ether was selected because it is unreactive with sodium metal and is capable of dissolving a sodium salt to form an electrolyte solution. A sodium salt is necessary to prevent contamination of the sodium metal product with another metal. In this environment the thin supported film of metal 16 employed, and which separates the anolyte portion 14 and catholyte portion 15, is mercury. The thin film of mercury 16 can be occasionally replenished if desirable by allowing mercury to trickle over the supporting material and through said solution from some source 17. Excess mercury may be removed from the electrolytic cell 11 through the drain 13.

Upon passage of an electric current through the anolyte portion 14 and catholyte portion 15 the following occurs in the anolyte portion: The anions are oxidized at the anode and chlorine gas is evolved from the solution and passes out of the cell through the gas dome 9. Sodium ions from the anolyte portion 14 are deposited upon and amalgamated into the thin supported film of mercury 16. The following occurs in the catholyte portion 15: Sodium ions are removed from the thin supported film of mercury 16 and migrate therethrough to the cathode 13. At the cathode 13, the ions are reduced to metallic sodium and, since the sodium metal is lighter than the solution, it floats to the surface of the catholyte portion 15 and is collected within the space 32 formed by the partial par-ti tion device 31. From there it is easily removed by overflowing from the electrolytic cell 11 through the riser 'pipe 12. In the event that a metal so treated is heavier than the catholyte 15, and is liquid at processing out of the cell through the gas dome 27.

I partition or film between the anode and cathode.

conditions it is conveniently collected at the bottom of the electrolytic cell 11 within a reservoir 19 and then withdrawn from the electrolytic cell 11.

In this embodiment, if it were desirable, the sodium metal amalgamated into the thin supported mercury film 16 could be conveniently reacted within the catholyte portion 15 to form suitable reaction products. For example, sodium hydroxide is conveniently produced by reaction of the sodium metal with water. A small amount of sodium hydroxide, since it is an electrolyte, can be added to water placed within the catholyte portion 15 for start up. Thereafter sodium hydroxide is produced from sodium metal obtained from a sodium chloride solution. Many other products can be produced as conveniently by reaction with a suitable material.

In the following description of the operation of a fusion type cell reference shall also be made to the pro cessing of sodium as in the foregoing but in this instance also, this description shall not be considered as limiting.

Referring to FIGURE 2, there is shown a half sectional view of an electrolytic cell 21 having a centrally located bottommounted anode 22 having a shell 23 concentric therewith and which also serves, in this particular embodiment, as the cathode, and a thin supported film of molten metal 26 which is also concentric with and interposed between the anode 22 and cathode 23. The anode and cathode are separated by electrical insulation 33 and ported film of metal is molten lead. Upon passage of an electric current therethrough the following occurs: In

the anolyte portion 24, chlorine gas is evolved and passed The sodium ions are issolved or deposited into a thin supported film of lead 26. In the catholyte portion 25, the sodium metal is removed from the thin supported film of lead 26. The sodium ions then migrate to the cathode 23 where reduction occurs and metallic sodium is produced. The

sodium metal flows to the surface of the molten bath and is easily removed by overflow from the cell through the conduit 28.

The following working examples are embodiments of the invention described in the foregoing. In all examples it is to be understood that a thin supported layer of liquid metal separates the anode and cathode compartments of the electrolytic cell. In all cases the supporting medium is one of such nature that the liquid or molten metal supported adheres, or wets, and substantially fills all of the openings within the supporting medium so as to form in essence a thin liquid metal The only reason for the existence of the said supporting medium is to support the said liquid metal partition. All concentrations are in proportions by weight and temperature are in degrees centigrade unless otherwise specified.

ExampIe I This example describes a continuous process for recovering substantially pure metallic sodium from a cell of the type shown by reference to FIGURE 1 and from a raw material consisting of an aqueous sodium chloride solution. The anode compartment is separated from the cathode compartment by a 35 mesh iron alloy screen which is wet with mercury.

A 10 percent aqueous sodium chloride solution is charged into the anode compartment of an electrolytic cell. The cathode compartment is charged with a 10 percent sodium iodide solution of diethylene glycol dimethyl ether, Current is passed through the electrolytic cell until the operating temperature of about 110 C. is reached. The potential drop between the anode and cathode is 10 volts. Substantially pure chlorine gas is evolved from the anode compartment and substantially pure metallic sodium is removed from the cathode compartment. The sodium rises along the cathode to the top of the cell where it is over-flowed and collected. The process is operated continuously by continuously charging sodium chloride into the anode compartment to maintain the desired concentration.

The following example describes a batch process for the production of substantially pure metallic sodium metal in solid form. The cell used is the same as in the foregoing example.

' Example II A 15 percent aqueous sodium chloride solution is charged into the anode compartment and an ethylene diamine solution, containing sodium bromide at 75 percent of saturation concentration, is charged to the cathode compartment. Current is passed through the cell and a potential of 10 volts is supplied between the anode and the cathode during operation. The operating temperature of the cell is 50 C. Substantially pure chlon'ne gas is evolved from the anode compartment and substantially pure metallic sodium is removed as a loose solid by scraping it from the cathode. After removal from the cathode the loose solid sodium particles are pumped out with the electrolyte stream to a place outside the cell walls where it is then filtered from the solution and melted.

Example III The foregoing example is repeated except that the operating temperature is maintained at 80 C. Sodium metal of high purity is obtained.

The following example describes a process for the manufacture of metallic sodium from a fused electrolyte bath. The anode and cathode compartments are separated by a 50 mesh iron alloy screen which is wet with molten tin.

Example IV A charge of 50 mole percent sodium chlorine and 50 mole percent calcium chloride is charged to both the anode and cathode comparment of the electrolytic cell. During operation fresh charges of the same materials are fed into the anode compartment as required. Current is passed through the cell by direct connections between the anode and .the cathode. The operating temperature of approximately 575 C. is reached within a relatively short time. The overall potential drop between the anode and cathode is 7.5 volts.

Substantially pure chlorine gas is evolved from the anode compartment. Sodium metal containing about percent calcium is collected from the top of the cathode compartment and removed from the electrolytic cell. The calcium is separated from the sodium by crystallization upon cooling as in the present commercial process.

The following example differs from this example only inasmuch as the supporting medium, and the film formed upon the supporting medium differs.

Example V The foregoing example is repeated except that a thin film of supported molten lead wets a 60 mesh nickel alloy wire screen and separates the anode and cathode compartments. Sodium metal of about 95% purity is againobtained.

Having described several methods for the production of a high purity of metallic sodium, methods will now be described for the production of reaction products of metals.

The following example describes a process for the production of sodium methylate of high purity. Reacting materials are added pari passu as the products are withdrawn. The anode and cathode compartments '6 are separated in the same manner as was described in Example I.

Example VI A 15 percent aqueous sodium chloride solution is charged into the anode compartment. A 5 percent solution of sodium methylate in anhydrous methyl alcohol is charged into the cathode compartment for start up. The cell is operated at a temperature of 'about 55 C. A potential drop of 4 volts is supplied between the anode and cathode. Substantially pure chlorine was obtained from the anode compartment. Sodium methylate of high quality was thereafter obtained from the reaction of sodium with the anhydrous methyl alcohol. When the concentration of sodium methylate has reached a concentration of 15 percent a product stream is withdrawn and sodium chloride added to the anode compartment in equivalent quantities.

The following example also describes a continuous process for the manufacture of sodium hydroxide. The anode and cathode compartments are separated by a mesh nickel alloy screen wetted with mercury.

In all instances in the following examples wherein hydrogen is generated, it is removed from the catholyte portion upon evolution from the liquid by means not shown.

Example VII An aqueous 15 percent sodium chloride solution is charged into the anode compartment and maintained at said concentration by addition of fresh sodium chloride to the anode compartment. Pure Water is charged into the cathode compartment and a small amount of sodium hydroxide added to form an electrolyte for start up. The cell is operated at a temperature of 65 C. After a short time from start up the concentration of the sodium hydroxide is approximately 70 percent. At this time there is begun a continuous withdrawal of some of the sodium hydroxide and water is added to the cathode compartment at the same volumetric rate in which the sodium hydroxide is removed. Sodium chloride is added to the anode compartment in quantities equivalent to the amount of sodium hydroxide withdrawn. A potential gradient of 4 volts is applied between the anode and cathode.

Example VIII The foregoing example is repeated except that the temperature of the cell is operated at a temperature of 80 C. Sodium hydroxide slightly in excess of 70 percent concentration is obtained.

The following example describes a continuous process for the manufacture of potassium hydroxide. The anode and cathode compartments are separated by a mesh stainless chrome steel screen wetted with mercury.

Example IX An aqueous 15 percent potassium chloride solution was supplied to the anode compartment and maintained at that concentration during the operation by addition of fresh sodium chloride to the anode compartment. Water is charged into the cathode compartment and a small amount of potassium hydroxide added to form an electrolyte for start-up. The cell is operated at a temperature of 75 C. After a short time from start-up the concentration of the potassium hydroxide within the cathode compartment is approximately 60 percent. At this time there is begun a continuous-withdrawal of some of the potassium hydroxide and fresh Water is added to the cathode compartment at the same volumetric rate in which the potassium hydroxide solution is removed. Potassium chloride is added to the anode compartment in quantities equivalent to the amount of potassium hydroxide Withdrawn from the cell. A potential gradient of 4.2 volts is applied between the anode and cathode during the operation.

I The following example describes a continuous process for the manufacture of lithium hydroxide. The anode and cathode compartments are separated by a 120 mesh Monel metal screen wetted with mercury.

Example X An aqueous percent lithium chloride solution is supplied to the anode compartment and maintained at that concentration during the operation by the addition of fresh lithium chloride to the anode compartment. Water is charged into the cathode compartment and a small amount of lithium hydroxide added to form an electrolyte. An electric current is passed through the cell and during operation an operating temperature of approximately 70 C. is maintained. After a short time from start-up the concentration of the lithium hydroxide within the catholyte compartment is approximately 10 percent. At this time there is begun a continuous withdrawal of some of the lithium hydroxide, and water is added to the cathode compartment at the same volumetric rate in which the lithium hydroxide is removed. Lithium chloride is added to the anode compartment in quantities equivalent to the amount of lithium hydroxide withdrawn from the cathode compartment. A potential gradient of 4.2 volts is applied between the anode and cathode during the operation.

Having discussed several reaction products of metals the following examples show methods for the production of metals of high purity other than sodium. The following example describes a continuous process for recovering substantially pure metallic potassium from an aqueous potassium chloride solution. The anode compartment is separated from the cathode compartment by a 120 mesh carbon steel (S.A.E. 10-10) screen which is wet with mercury.

Example XI metal rises along the cathode to the top of the cell where it is overfiowed and collected. Potassium chloride in equivalent quantities to the amount of potassium removed from the cathode compartment is charged into the anode compartment to maintain the desired concentration.

The following'example describes a process for the manufacture of metallic zinc. The anode and cathode compartments are separated by a 100 mesh stainless chrome steel screen wet with mercury.

Example XII An aqueous solution, containing 12 percent sodium chloride and 7 percent zinc chloride is charged into the anode compartment. The pH of the solution therein is controlled at about 6 during the operation by the addition of small amounts of hydrochloric acid. A diethylene glycol dimethyl ether solution, 75 percent saturated with zinc bromide, is charged into the cathode compartment. During the operation the cell is maintained at a temperature of 60 C. and a potential drop of 10 volts is supplied between the anode and cathode. Substantially pure chlorine gas is evolved from the anode compartment and solid sodium and zinc are removed from the cathode compartment by scraping. The mixed metal is pumped out of the cathode compartment with the electrolyte. The sodium and zinc are then separated by melting the metals, crystallizing out the zinc by cooling, and then filtering.

The following example describes a continuous process for the production of metallic magnesium metal. The

anode and cathode compartments are separated by a 50 mesh stainless chrome steel screen wet with molten lead.

Example XIII An eutectic mixture of sodium chloride and magnesium chloride is charged into both the anode and cathode compartments. A potential of 6 volts is applied between the anode and cathode. Current is passed through the cell until the operating temperature of approximately 700 C. is attained. Substantially pure chlorine gas is evolved from the anode compartment and a molten mixture of sodium and magnesium is collected from the top of the cathode compartment and removed from the electrolytic cell.

The magnesium metal is separated from the sodium metal by fractional crystallization and filtering as in the foregoing example.

The following example also describes a process for the continuous production of calcium metal within a fused bath. The anode and cathode compartments are separated by a 50 mesh nickel alloy screen wetted with molten silver.

Example XIV A charge of essentially pure calcium chloride is charged into both the anode and the cathode compartments. A potential gradient of 8 volts is supplied between the anode and cathode. Upon passage of an electric current through the cell, substantially pure chlorine is evolved from the anode compartment and substantially pure metallic calcium from the cathode compartment. The tem perature is maintained during the operation at l,O00 C. Fresh calcium chloride is charged to the anode and cathode compartments intermittently as desired.

The following examples describe processes for organic reduction reactions. The example immediately following describes a method for the production of sodium sulfide. The anode and cathode compartments are separated by a mesh monel metal screen wetted with mercury.

Example XV A 15 percent aqueous sodium chloride solution is supplied to the anode compartment and maintained at that concentration during the operation by addition of fresh sodium chloride therein. A 20 percent aqueous polysulfide solution is charged into the cathode. An equal volumetric quantity of liquid is also removed from another portion of the cell compartment as a stream. A constant liquid level is maintained within the cathode compartment. The stream withdrawn from the cathode compartment contained approximately 30 percent sodium sulfide. The operating temperature of the cell is maintained at 60 C. and a potential gradient of 4 volts is supplied between the anode and cathode.

Preferably the sodium polysulfide solution corresponds to the formula Na S The flow rate into and leaving the cathode compartment must be controlled within certain limits in order not to completely strip the sodium from the thin supported film of mercury, or amalgam, otherwise some mercury sulfide will form. Flow rates will, of course, depend upon the volumetric capacity of the electrolytic cell. For the production of sodium sulfide of the highest purity and whitest color, it is essential to exclude air from the process, which otherwise oxidizes the sodium sulfide to sodium thiosulfate. sary to avoid contamination with such metals as iron, lead and zinc.

The following example describes a process for the production of sodium hydrosulfite. The anode and cathode compartments are separated by a mesh nickel alloy screen wetted with mercury.

Example XVI A 15 percent aqueous sodium chloride solution is supplied to the anode compartment. An aqueous solution of sodium thiosulfate and sodium sulfite in 10:1 pro- It is also necesportions is supplied to the cathode compartment. Sulphur dioxide gas is bubbled into the solution within the cathode compartment so as to maintain the pH of the solution between and 7. A potential of 4 volts is applied between the anode and cathode and the operating temperature of the cell is maintained at 40 C. Upon passing an electric current through the cell crystals of sodium hydrosulfite with two waters of hydration is formed in the cathode compartment. The contents of the cathode compartment are then discharged and the crystals are removed by filtering.

The contents of the cathode compartment can be removed more or less continuously if desired. A stream can be withdrawn from the cathode compartment, crystals removed continuously in a filter press, and the liquid portion treated with make-up quantities of reactants and returned to the cell. The dihydrate crystals can be dehydrated by heating rapidly to a temperature of from about 60 to about 65 C., after which they are filtered, washed with alcohol and dried under vaccum.

The following example describes a process for the production of sodium chlorite. The separation of the anode and cathode, potential gradient between the anode and cathode, temperature of operation, and charge within the anode compartment are the same as in the foregoing example.

Example X VII The cathode compartment is charged With a 0.1 normal aqueous sodium hydroxide solution, and while the cell is in operation, chlorine dioxide, diluted with 6 times its volume of air, is bubbled through the water. The solution is maintained on the alkaline side during the reaction by the addition of enough sodium hydroxide to keep the solution approximately 0.1 normal. Sodium chlorite forms in the solution.

The contents of the cathode compartment after completion of the operation is evaporated and the chlorite recovered.

The following example describes a process for the production of azobenzene. Separation of the anode and cathode compartments and charge to the anode compartment are the same as in the foregoing example.

Example XVIII A 20 percent suspension of nitrobenzene in a 30 percent aqueous sodium hydroxide solution is charged into the cathode compartment. A potential of 4 volts is supplied between the anode and cathode and the temperature of operation is maintained at 100 C. After the reaction is completed, the contents of the cathode compartment is run into a heated steel tank where it separates into two layers. The upper layer is principally azobenzene and the lower layer is an impure caustic solution containing about 50% sodium hydroxide. The latter is not of standard purity, but can be used for many purposes. The other product of the process can be purified in the normal commercial manner. It contains the following:

Percent Azobenzene 80 Azoxybenzene Hydrazobenzene 8 Aniline 2 In the following three examples, the separation of the anode and cathode, the potential gradient between the anode and cathode, the temperature of operation, and the charge within the anode compartment are the same as in Example XVI. The example immediately following describes a process for the production of glyoxalic acid.

Example XIX A 0.1 normal hydrochloric acid solution containing oxalic acid is charged into the cathode compartment and an electric current passed through the cell. The oxalic acid is converted into glyoxalic acid. When the concentration thereof within the cathode compartment is 10 percent a fresh stream of 0.1 normal hydrochloric acid containing oxalic acid is charged thereto and a stream of the same volumetric quantity is withdrawn from another portion of the cathode compartment. The liquid level within the cathode compartment is maintained and a residence time is established therein such that a 10 percent solution of glyoxalic acid in 0.1 normal hydrochloric acid is continuously withdrawn. The glyoxalic acid is recovered therefrom as in the normal commercial operation.

The following example describes the process for the production of pinacol from acetone.

Example XX The cell is placed in operation and an equilibrium eventually obtained as in the above example. A 5 percent pinacol aqueous sodium hydroxide solution is maintained within the cathode compartment. A stream of the same composition is continually withdrawn from the cath ode compartment and a stream of the same volumetric quantity, containing acetone and water, is continuously added. The products from the cathode compartment are separated as in the normal commercial operations.

The following example describes a continuous process for the production of hydroquinone.

Example XXI An equilibrium is set up within the cathode compartment of the cell as in the foregoing examples. A 5 percent hydroquinone aqueous sodium hydroxide solution is maintained within said cathode compartment and a product stream of the same composition is withdrawn therefrom. A second stream of the same volumetric quantity, containing quinone and water, is added thereto. The products of the reaction are separated as in conventional commercial operations.

From the foregoing, it is apparent that many variations of the process and apparatus of this invention are possible. Obviously, many reactions may be carried out without departing from the spirit and scope of the invention. The process may be carried out in cells operating at high temperatures, as in fusion cells, or at cooler temperatures wherein solutions of electrolytes are employed.

The nub of the process is the separation of the anode compartment from the cathode compartment by a thin supported film of a metal, unreactive with the electrolyte bath and liquid at processing conditions, and which is capable of dissolving the metal of the salt within the anode compartment which is to be processed. The solubility of the metals within the said supported film of metal need not be very high at the operating temperatures. Usually if the metal of the salt to be processed is as much as about 0.1 percent soluble in the supported film of metal at the lower operating temperatures the process can be conveniently carried out. At higher temperatures the solubility of the metal of the salt to be processed can be even less soluble in the metal film because of the rapid rate of diffusion at the higher temperatures. Many metals whose solubility is as low as about 0.02 percent soluble in the film may be thus processed. The limitations as to diffusion rates are largely hypothetical and principally de termined by economics. A wide variety of metals can be processed by use of this invention. When using a thin film of supported mercury for example, even at temperatures as low as from about 15 to 20 0, solutions of salts of the following metals can be conveniently processed; thallium, cadmium, cesium, zinc, bismuth, lead, rubidium, strontium, tin, sodium, potassium, barium, calcium, and magnesium. The salts of many other metals can also be processed. This is especially true at higher operating temperatures. This is true even of metals which 11 process offers a method for the separation of the metals of salts which are insoluble in the supported film of metal from the metals of salts which are soluble therein. This is because the salts of the soluble and insoluble metals can be placed within the anolyte portion and only the metal which is soluble in the supported film can diffuse therethrough. For example, arsenic, beryllium, cobalt, chromium, iron, gallium, germanium, molybdenum, nickel, antimony, titanium, tungsten, vanadium, uranium, and zirconium are insoluble in mercury and the metals of such salts can be separated from the metals of salts which are amalgamatable, the non-amalgamatable metal being left in the anode compartment and the amalgamatable metal being recovered in the cathode compartment. Obviously also, conditions of solubility can be controlled largely by the temperature of operation of the cell. As has been stated, all that is required to obtain pure metals at the cathode is to furnish a catholyte which is non-reactive with the metal product desired and to form the said catholyte by dissolving therein a salt, the metallic portion of which is the same as the metallic product desired.

Reaction products of the processed metal can be obtained by supplying a catholyte which reacts therewith to form the desired product. For example, caustic alkalis can be produced by forming an anolyte portion of an alkali salt, the metallic portion of which can be reacted with water supplied to the cathode compartment. Alcoholates can be similarly prepared by reacting the metal with a suitable anhydrous alcohol. Various metallic salts can be produced by the direct reaction of the metal dissolved in the thin supporting film of metal with other elements and acidic compounds dependent upon the product desired. For example, sodium sulfide can be produced within the cathode compartment by reaction of metallic sodium with sulphur; sodium hydrosulfite by reaction of sodium with sulphur dioxide; zinc hydrosulfite can be prepared in similar manner; sodium chloride by reaction of sodium with chlorine dioxide; sodium nitrite by reaction of sodium with nitrogen peroxide. It is also quite possible to carry out a large number of organic reductions within the cathode compartment. Most organic reductions make use of the nascent hydrogen produced within the cathode compartment by certain reactions; for example, the reaction of sodium with an aqueous catholyte containing nitrobenzene to produce principally azobenzene.

When using the process of the invention a very wide range of temperature selections are possible. One important factor is that the temperature must be high enough to keep the thin supported film of metal liquid and unreactive. Metals can of course be selected which will fit the temperature of the process. Metals can be selected for this purpose which can be used at very low temperatures, for example mercury. Other metals can also be employed which are liquid at very high temperatures, those temperatures required to produce fusion of many systems. It is also quite possible to use alloys of metals for this purpose. Temperature is also governed by the nature of the material to be processed. In fusion cells the temperature must be high enough to fuse, or liquefy, the material to be treated. In the treatment of liquid solutions, as for example where a salt is dissolved in water, the temperature can even be almost cold. Solubilities of compounds, both as to the material to be treated and as to the product, or products, formed must also be considered in selecting a preferred operating temperature.

When employing the process to produce pure metals from ordinary solutions it is generally desirable to operate at a temperature of from about 40 C. to about 110 C. Of course, since the number of metals which can be processed are very numerous, the preferred ranges of temperature is dependent upon the metal to be processed. The same can be said of the selection of a preferred electric potential gradient through the solution. Generally no direct electric potential is supplied to the metal film, but this can be done if desired. If a potential be supplied between the anodeand cathode there is a potential drop through the whole solution between these electrodes. There is also a drop between either electrode and the supported metal film which, in this case, is a function of its distance between these electrodes.

When employing the process of the invention to manufacture metallic sodium from an electrolyte solution, which is recovered in liquid form, the operating temperature is generally within a range of from about 100 C. to 130 C. and preferably within a range of from about 100 to 105 C. When recovering metallic sodium from an electrolyte solution, and as a solid, the operating temperature is generally within a range of from about 40 C. to 95 C. and preferably within a range of from about 60 to 85 C. In both cases, the electric potential supply between the anode and cathode is generally from about 5 to 10 volts, and preferably is maintained at approximately 7 volts.

When the process is employed to manufacture metallic zinc from an aqueous electrolyte solution, the temperature is generally maintained within a range of from about 40 C. to C., and preferably within a range from about 50 C. to 70 C. The electric potential gradient between the anode and cathode is generally from about 3 to 8 volts, and preferably is maintained at approximately 6 volts. When producing metallic potassium the temperature is generally maintained within a range of from about 65 to 110 C. and preferably within a range of from about 70 to 80 C. The electric potential gradient between the anode and cathode is generally from about 4 to 20 volts, and preferably is maintained at approximately 10 volts. In the production of metals from fused mixtures of their salts in accordance with the principles stated heretofore the only requisite of temperature is that the temperature be sufficient to produce said molten mixture and to maintain the thin supported film of metal in a liquid condition.

When employing the process of the invention to manufacture caustic alkalis from an electrolyte solution, generally the temperature range of operation is controlled between about 40 and 110 C. A high temperature is preferred when manufacturing lithium hydroxide because of its lower solubility in an aqueous solution. Specifically, when manufacturing sodium hydroxide it is preferable that the operating temperature be maintained between about 60 and C. When manufacturing potassium hydroxide the preferred operating temperature is between about 65 and C.; and for lithium hydroxide a range of from about 80 C. to C. In all cases, when manufacturing caustic alkalis the electric potential gradient between the anode and cathode is from about 2 to 6 volts, and preferably between about 3 and 5 volts.

The alcoholates are prepared by furnishing the appropriate anhydrous alcohol within the cathode compartment and by supplying the salt of the desired metal into the anode compartment. The lower anhydrous aliphatic alcohols react with the metal in much the same manner as water is used to produce caustic alkalis. This is especially true of methyl alcohol and ethyl alcohol. It is important that the alcohols be anhydrous; otherwise the alcoholates will hydrolyze to form a hydroxide. Solutions of sodium methylate and methanol, for example, can be prepared in the range of from about 5 to 15 percent sodium methylate. Potassium alcoholates can be produced in the same manner as sodium alcoholates. The only requisite to prepare alcoholates in this manner is that the metal be reactive with the anhydrous alcohol at moderate temperatures, temperatures below the boiling point of the alcohol.

As was mentioned, various metallic salts can be produced by the direct union of the metal dissolved within the amalgam with other elements and acidic compounds. These processes are generally carried out at relatively supplied between the anode and cathode.

low temperatures. In the production of sodium hydrosulfite it is preferred that the maximum operating temperature of the cell be maintained at below 40 C. It is essential that the pH of the solution be maintained on the acid side for best results, preferably between and 7. Generally, a voltage of between about 3 and 4 is In addition to preparing sodium hydrosulfite in the manner described heretofore, zinc hydrosulfite can be produced in similar fashion. The method hereindefined for the production of sodium sulfide from a sodium polysulfide solution is sufficient to produce sodium sulfide solutions containing up to about 30 percent by weight sodium sulfide.

As was stated heretofore, various organic reductions are also possible. This is because certain metals will produce nascent hydrogen when reacting with the catholyte portion. Thus, metallic sodium or potassium will react with water to produce nascent hydrogen which is then available for the reduction of various compounds. In these instances caustic alkalis are produced as a byproduct.

The materials of construction for the anode and cathode are the same as in ordinary electrolytic cells. For example, the cathode is usually composed of iron or steel and the anode is usually graphite. In a preferred embodiment the outer shell will serve as the cathode and the anode (or anodes) is formed by a bottom centrally mounted graphite stick or bar. A supported thin film of metal completely surrounds and separates the anode from the cathode. The supporting material for the thin film of metal will vary somewhat depending upon its specific environment. For example, if the supporting material is to be used in a high temperature fusion bath and is to support a thin film of a particular molten metal the supporting material must be of such nature that it will withstand the high temperature and also must be capable of adhesion with the molten metal. In other words, the materials selected for the support must be capable of being wetted by the molten metal. The holes, pores, or openings within the supporting material must be small enough that the said openings are completely filled or substantially completely filled, with the molten metal. Generally the holes or openings within the supporting material should be no larger than the holes or openings provided within a 35 mesh screen.

Obviously, however, this is dependent upon the nature of the supporting material and its capacity of being wetted by the supported metal. Preferably the openings within the supporting material should be within a range equivalent to that furnished by a 50 to 150 mesh screen. Examples of materials which are useful for such purposes are: steel or iron, alloyed with at least about 0.01% weight metallic sodium or other alkali metal, or any other material which can be wet by, and will support a thin layer of metal. The following supporting materials may be used to form a thin mercury film; stainless chrome steel, containing an approximate minimum concentration of 0.05 percent by weight sodium or at least 0.15 percent weight potassium. Monel metal, carbon steel (S.A.E. 10), and nickel containing at least approximately 0.01 percent by weight sodium or at least about 0.10 percent, 0.05 percent, 0.02 percent approximate minimum concentration of potassium will also support mercury. In general, the alloys wet by mercury will also be wet by silver, tin and lead.

Having defined the invention and its best modes of operation what is claimed is:

1. An electrolysis process for producing an alkali metal comprising maintaining an electrolyte bath having a first electrolyte and a second electrolyte, the said first electrolyte, consisting essentially of an alkali metal chloride in water, being in contact with an anode and said second electrolyte being in contact with a cathode which is incapable of alloying with the alkali metal produced, the said second electrolyte consisting essentially of (a) an alkali metal iodide dissolved in diethylene glycol dimethyl ether, and being (b) contiguous to the first electrolyte; maintaining said first electrolyte and second electrolyte divided by a thin vertically supported stationary film of metallic mercury; passing an electric current through the electrolyte bath so that the alkali metal of the alkali metal chloride dissolved in the first electrolyte is electrolytically dissolved into the thin mercury film and concurrently the so-deposited alkali metal is electrolyzed from said mercury film into the said second electrolyte and thence upon the cathode; and then removing the alkali metal from the second electrolyte.

2. An electrolysis process for producing sodium comprising maintaining an electrolyte bath having a first electrolyte and a second electrolyte, the said first electrolyte, consisting essentially of sodium chloride in water, being in contact with an anode and said second electrolyte being in contact with a cathode which is incapable of alloying with the sodium produced, the said second electrolyte consisting essentially of (a) sodium iodide dissolved in diethylene glycol dimethyl ether, and being (b) contiguous to the first electrolyte; maintaining said first electrolyte and second electrolyte divided by a thin vertically supported stationary film of metallic mercury; passing an electric current through the electrolyte bath so that the sodium of the sodium chloride dissolved in the first electrolyte is electrolytically dissolved into the thin mercury film and concurrently the so-deposited sodium is electrolyzed from said mercury film into the second electrolyte and thence upon the cathode; and then removing the sodium from the second electrolyte.

References Cited in the file of this patent UNITED STATES PATENTS 590,548 Keller Sept. 21, 1897 631,468 Keller Aug. 22, 1899 759,799 Blackmore May 10, 1904 1,109,311 Allen Sept. 1, 1914 1,538,390 Ewan May 19, 1925 2,351,383 Wolf June 13, 1944 2,615,838 Minnick et al Oct. 28, 1952 FOREIGN PATENTS 553,897 Great Britain June 9, 1943 772,359 Great Britain Apr. 10, 1957 490,911 Great Britain Aug. 23, 1938 17,169 Great Britain of 1892 

1. AN ELECTROLYSIS PROCESS FOR PRODUCING AN ALKALI METAL COMPRISING MAINTAINING AN ELECTROLYTE BATH HAVING A FIRST ELECTROLYTE AND A SECOND ELECTROLYTE, THE SAID FIRST ELECTROLYTE, CONSISTING ESSENTIALLY OF AN ALKALI METAL CHLORIDE IN WATER, BEING IN CONTACT WITH AN ANODE AND SAID SECOND ELECTROLYTE BEING IN CONTACT WITH A CATHODE WHICH IS INCAPABLE OF ALLOYING WITH THE ALKALI METAL PRODUCED, THE SAID SECOND ELECTROLYTE CONSISTING ESSENTIALLY OF (A) AN ALKALI METAL IODIDE DISSOLVED IN DIETHYLENE GLYCOL DIMETHYL ETHER, AND BEING (B) CONTIGUOUS TO THE FIRST ELECTROLYTE, MAINTAINING SAID FIRST ELECTROLYTE AND SECOND ELECTROLYTE DIVIDED BY A THIN VERTICALLY SUPPORTED STATIONARY FILM OF METALLIC MERCURY, PASSING AN ELECTRIC CURRENT THROUGH THE ELECTROLYTE BATH SO THAT THE ALKALI METAL OF THE ALKALI METAL DISSOLVED INTO THE THIN MERCURY FILM AND CONCURRENTLY THE SO-DEPOSITED ALKALI METAL IS ELECTROLYZED FROM SAID MERCURY FILM INTO THE SAID SECOND ELECTROLYTE AND THENCE UPON THE CATHODE, AND THEN REMOVING THE ALKALI METAL FROM THE SECOND ELECTROLYTE. 